Members of the Mollie's pack surround a bison in this February 2005 photograph. The wolves try to harass the bison into deeper snow, where the bison are less of a threat and easier to attack.

Yellowstone's Junction Butte wolf pack failed in a recent attempt to kill a bison, but the pack appears to be thriving again after the death of its former alpha female, Wolf 907F.

Yellowstone's Junction Butte wolf pack failed in a recent attempt to kill a bison, but the pack appears to be thriving again after the death of its former alpha female, Wolf 907F.

MAMMOTH HOT SPRINGS (AP) Yellowstone National Park wolves have begun preying upon bison more, according to biologists. Elk meat has made up about 90 percent of the wolves diet since wolf ...